Roberts Tara L, Dunn Jasmyn A, Terry Tamsin D, Jennings Michael P, Hume David A, Sweet Matthew J, Stacey Katryn J
Institute for Molecular Bioscience, University of Queensland, Brisbane, Australia.
J Immunol. 2005 Sep 15;175(6):3569-76. doi: 10.4049/jimmunol.175.6.3569.
Bacterial DNA activates mouse macrophages, B cells, and dendritic cells in a TLR9-dependent manner. Although short ssCpG-containing phosphodiester oligonucleotides (PO-ODN) can mimic the action of bacterial DNA on macrophages, they are much less immunostimulatory than Escherichia coli DNA. In this study we have assessed the structural differences between E. coli DNA and PO-ODN, which may explain the high activity of bacterial DNA on macrophages. DNA length was found to be the most important variable. Double-strandedness was not responsible for the increased activity of long DNA. DNA adenine methyltransferase (Dam) and DNA cytosine methyltransferase (Dcm) methylation of E. coli DNA did not enhance macrophage NO production. The presence of two CpG motifs on one molecule only marginally improved activity at low concentration, suggesting that ligand-mediated TLR9 cross-linking was not involved. The major contribution was from DNA length. Synthetic ODN >44 nt attained the same levels of activity as bacterial DNA. The response of macrophages to CpG DNA requires endocytic uptake. The length dependence of the CpG ODN response was found to correlate with the presence in macrophages of a length-dependent uptake process for DNA. This transport system was absent from B cells and fibroblasts.
细菌DNA以TLR9依赖的方式激活小鼠巨噬细胞、B细胞和树突状细胞。尽管含短链ssCpG的磷酸二酯寡核苷酸（PO-ODN）可模拟细菌DNA对巨噬细胞的作用，但它们的免疫刺激作用远低于大肠杆菌DNA。在本研究中，我们评估了大肠杆菌DNA与PO-ODN之间的结构差异，这可能解释了细菌DNA对巨噬细胞的高活性。发现DNA长度是最重要的变量。双链性并非长DNA活性增加的原因。大肠杆菌DNA的DNA腺嘌呤甲基转移酶（Dam）和DNA胞嘧啶甲基转移酶（Dcm）甲基化并未增强巨噬细胞NO的产生。一个分子上存在两个CpG基序在低浓度时仅略微提高活性，这表明不涉及配体介导的TLR9交联。主要贡献来自DNA长度。大于44 nt的合成ODN达到了与细菌DNA相同的活性水平。巨噬细胞对CpG DNA的反应需要内吞摄取。发现CpG ODN反应对长度的依赖性与巨噬细胞中存在的DNA长度依赖性摄取过程相关。B细胞和成纤维细胞中不存在这种转运系统。
